The present invention relates to sensors for the detection of an analyte and, particularly, to sensors for the detection of hazardous or toxic analytes.
References set forth herein may facilitate understanding of the present invention or the background of the present invention. Inclusion of a reference herein, however, is not intended to and does not constitute an admission that the reference is available as prior art with respect to the present invention.
There are many types of sensors designed to detect the presence of chemical species, for example, on surfaces or within solutions. Such sensors exhibit signals based on a wide variety of chemical, electrical, or physical responses. Many such sensors are based upon “negative responses”. In negative response sensors, the chemical analyte of interest inhibits or retards a chemical or physical process that would otherwise take place within the sensor in the analyte's absence. The term “negative response sensor” thus generally refers to sensors in which the presence of a target analyte results in the absence of or the reduction of a signal change or a signal change.
Enzymatic proteins are remarkable natural catalysts in that they selectively catalyze many reactions under relatively mild reaction conditions. Enzymes also offer the potential to perform sterio- and regio-selective reactions not readily accomplished with conventional chemistry. As used herein, the term “enzyme” refers generally to proteins that catalyze biochemical reactions. These “biopolymers” include amide-linked amino acids and typically have molecular weights of 5,000 or greater. A compound for which a particular enzyme catalyzes a reaction is typically referred to as a “substrate” of the enzyme.
In general, six classes or types of enzymes (as classified by the type of reaction that is catalyzed) are recognized. Enzymes catalyzing reduction/oxidation or redox reactions are referred to generally as EC 1 (Enzyme Class 1) Oxidoreductases. Enzymes catalyzing the transfer of specific radicals or groups are referred to generally as EC 2 Transferases. Enzymes catalyzing hydrolysis are referred to generally as EC 3 hydrolases. Enzymes catalyzing removal from or addition to a substrate of specific chemical groups are referred to generally as EC 4 Lyases. Enzymes catalyzing isomeration are referred to generally as EC 5 Isomerases. Enzymes catalyzing combination or binding together of substrate units are referred to generally as EC 6 Ligases.
Enzymes have been known since the early 1960's to be useful tools for detecting the presence of chemical species. Rogers, K. R., Biosensors Bioelectronics, 10, 533 (1995). A number of enzymatic biosensors have been designed to detect a variety of different compounds including, for example, glucose, creatinine, urea, and cholinesterase inhibitors. Parente, A. H., Marques, E. T. Jr., Appl. Biochem. Biotechnol. 37, 3, 267 (1992); Yang, S., Atanasov, P., Wilkins, E., Ann. Biomed. Eng., 23, 6, 833 (1995). U.S. Pat. No. 5,858,186 describes a urea-based biosensor in which substrate hydrolysis is monitored with a pH electrode. U.S. Pat. Nos. 5,945,343 and 5,958,786 describe enzyme-based polymer sensors which fluoresce in the presence of ammonia, which is enzymatically produced from urea and creatinine respectively. In addition U.S. Pat. No. 4,324,858 describes the utilization of cholinesterase for the colorimetric detection of organophosphorus pesticides and nerve agents. A related patent, U.S. Pat. No. 4,525,704 describes the use of cholinesterases and electrical currents in detecting toxic gases.
Generally, enzymatic biosensors function by one of two methods: (1) the sensing enzyme converts an otherwise undetectable compound into another or series of compounds which can be detected by visual, chemical, or electrical techniques; or (2) the enzyme is inhibited by the presence of the compound of interest and enzyme inhibition is linked to a measurable quantity.
Independent of the method of use, the signals of enzyme-based biosensors are often limited in practical application by the nature of enzyme activity. Like non-enzymatic sensors, most enzymatic sensors are negative response sensors. For example, in many enzymatic sensors the sensor provides a positive response in the presence of target analyte only in the case that the target analyte is a substrate for the enzyme of the sensor. In other words a noticeable change in the sensor indicates the presence of a target analyte. If the detection of enzyme inhibitors or the detection of substrate deficiency is desired, existing approaches rely on negative response signals, or the absence or reduction of an enzymatic reaction, to indicate the presence of inhibitors or the absence of target compounds.
U.S. patent application Ser. No. 09/858,686, filed May 7, 2001 and entitled Positive Response Biosesensors and Other Sensors, assigned to the assignee of the present invention, the disclosure of which is incorporated herein by reference, discloses sensors and methods in which the non-intuitive nature of a previously negative response sensors are changed to a more intuitive, positive response system. The methods and devices of U.S. patent application Ser. No. 09/858,686 are, for example, well suited for application in enzymatic biosensors and enzymatic biosensing methods.
It is very desirable to further develop sensors and sensing method through which the non-intuitive nature of negative response enzymatic and other sensors can be changed to a more intuitive positive response system.